One problem associated with some electronic devices is the undesirable production of high-frequency electromagnetic radiation which can interfere with the proper operation of other electronic equipment. Such electromagnetic radiation is known as electromagnetic interference (“EMI”). To ensure that electronic devices do not emit excessive amounts of EMI so as to interfere with the operation of other adjacent electronic devices, the United States Federal Communications Commission has promulgated regulations which limit the amount of EMI that can be emitted from many electronic devices. Electronic devices which do not comply with the FCC regulations cannot be legally sold in the United States. The governments of many other countries have similar regulations.
Most of today's digital computer equipment operates at switching frequencies which generate electromagnetic radiation that can lead to EMI. One such example includes high-speed disk drives with data transfer rates of at least 1 Gigabit per second (“Gbps”). In addition to producing electromagnetic radiation at the frequency of the data transfer rate, harmonic frequencies are also produced. Thus, for a high-speed disk drive whose integrated data input/output circuitry operates at a data transfer rate of 4.25 Gbps, the EMI includes significant components at a fundamental frequency of 4.25 GHz and its clock harmonic frequencies of up to 8.5 GHz.
Since the switching frequency of hard disk drives cannot be reduced and still obtain high performance, the most practical and feasible solution to the problem of the emitted EMI is to contain that EMI. One method for containing undesirable electromagnetic radiation is to use an EMI shield (or Faraday cage). The EMI shield encloses the electronic device which produces the undesirable electromagnetic radiation and prevents the EMI from propagating beyond the enclosure. A typical EMI shield is made of a metallic material which blocks the direct passage or propagation of the undesirable electromagnetic radiation. The EMI shield attenuates the EMI to reduce its strength and/or prevent it from escaping into the immediate environment to interact with adjacent electronic devices and interfere with their proper operation.
Effective EMI shields are typically created from a material which is highly conductive of electromagnetic radiation. For high-speed hard disk drives, the hard disk drive is enclosed within a disk drive carrier device that is made almost entirely from metal. The metal becomes the EMI shield to attenuate and contain the emitted EMI.
Although metal disk drive carriers are effective in containing and suppressing the EMI, the use of metal in the carrier device increases its manufacturing cost. Constructing the disk drive carrier from less-expensive, non-metallic materials, such as plastic, fails to block the emitted electromagnetic radiation sufficiently to the achieve an acceptable level of EMI established by applicable governmental regulations.